Magnetic Anisotropy of Mn12-acetate Nanomagnets from High-field Torque Magnetometry

The zero-field splitting (zfs) parameters of the ground S = 10 state in the easy-axis mol. nanomagnet [Mn12O12(OAc)16(H2O)4]·2AcOH·4H2O were detd. by cantilever torque magnetometry (CTM) in high magnetic fields. Torque curves were recorded in the superparamagnetic regime (4.2 K) by applying the magnetic field (0-28 T) very close to the hard magnetic plane of a single-crystal sample. The 2nd- and 4th-order anisotropy parameters obtained by this procedure [α=-0.389(5) cm-1 and β=-8.4(5)×10-4 cm-1 in the spin-Hamiltonian Hzfs = αSz2+βSz4+γ(S+4+S-4)] are in excellent agreement with those detd. by spectroscopic techniques, such as high-frequency EPR and inelastic neutron scattering. High-field CTM provides a simple macroscopic method for studying magnetic anisotropy in high-spin mols.